An expression of all out joy, similar to the joy expressed by a small child. It is often accompanied by a celebratory gesture of fist-shaking similar to the victory dance of a retarded child, or a person with special needs.

"Dude! Did you see that?! That was a fucking awesome score!"
"SIPPYCUP!"

Juvenile or immature. From the popular children's drinking device 'a sippy cup', made with a covered lid with narrow built-in sipping slot to prevent spillage. Toddlers drink the beverage inside via the narrow slot, and the drink is almost impossible for them to spill because of the cup's design.

"God, look at those girls over there wearing Elmo-t-shirts at the mall. What, are they six or something?"
"Yeah, like that is so sippy cup already."

or

"What was it with rappers all wearing pacifiers and baggy toddler clothes a few years ago?"
"Yeah! Like was that sippy cup, or what?"

after ejaculating into your partners mouth, they spit back out the seman on to your erect penis....and then suck up or sip it back up into their mouth...giving the illlusion of drinking through the straw of a childs sippy cup!

Dude that after that Dawn girl gave me the best hummer of my life, she spit out my jizz back onto my cock and slurped it back up like juice out of a sippy cup!